The global acrylic market is very large and it is expected to grow at a moderate rate to nearly 20 billion dollars per year by the end of the next decade at a CAGR (Compound Annual Growth Rate) of about 6%. The acrylic acid market by derivative type is segmented into acrylic esters, acrylic polymers, and other derivatives. The main driver of the market is the use of this precursor chemical in absorbent applications, with end-user markets in diapers, surface coatings, adhesives and sealants, plastic additive industry, water treatment industry, textiles, surfactants, and others. Currently, acrylic acid is heavily consumed in manufacturing diapers as polyacrylic acid and cross-linked polyacrylic acid, super absorbent polymers. Diapers are the fastest growing segment, at CAGR of 7.7%, and is expected to dominate the global acrylic acid market beyond 2020. Increasing geriatric population in the U.S. and Canada are projected to drive adult incontinence products demand. Geographically, the Asia Pacific market is projected to lead the global industry. Industrially important acrylate esters include methyl acrylate, butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate and others.
Inexpensive feedstocks derived from petrochemicals have sustained the production of plastic materials on a massive scale, but the limited nature of these resources has necessitated the development of synthetic routes derived from renewable resources. Stringent government regulations pertaining to the environmental safety and human health, and volatile prices of the raw materials are restricting the growth of the acrylate market globally. A key challenge lies not only in finding a viable route from renewable feedstocks, but also in developing an overall process that itself is sustainable, of low environmental impact, and economically competitive with traditional petroleum products (Hillmyer, M. A. Science (2017) 358:868-870). In this regard, lactic acid has shown particular promise given its ready availability from carbohydrates via fermentation (Bicker, M. et al, J. Mol. Catal. A (2005) 239:151; Holm, M. S. et al, Science (2010) 328:602; Kishida, H. et al, Carbohydr. Res. (2006) 341: 2619; Zeng, W. et al, Catal. Lett. (2009) 133:221; Rasrendra, C. B. et al, J. Chem. Sus. Chem (2011) 4:768) and its facile conversion into a number of commodity chemicals including polylactide (Mäki-Arvela, P. et al, Chem. Rev. (2014) 114:1909-1971; Chen, G. Q. et al, Chem. Rev. (2012) 112:2082-2099).
Direct conversion of lactic acid and the corresponding alkyl lactates into acrylic acid and acrylate esters, respectively, has been reported (U.S. Pat. Nos. 2,859,240; 4,729,978; US 2017/0057900; Zhang, J. et al, Can. J. Chem. Eng. (2008) 86:1047-1053; Zhang, Z. et al, Ind. Eng. Chem. Res. (2009) 48:9083-9089; US 2014/0155653; JP 2014189513 A; Tang, C. et al, Catalysis Communications (2014) 43:231-234; Blanco, E. et al, Applied Catalysis B: Environmental (2016) 180:596-606; Yan, B. et al, ACS Catal. (2014) 4:1931-1943). One such route is the direct dehydration of lactic acid using alkali and alkali earth metal catalysts (U.S. Pat. No. 5,252,473). However, these routes generally suffer from limited conversions and yields (Zhang, J. et al ACS Catal. (2011) 1:32; Sun, P. et al, Ind. Eng. Chem. Res. (2010) 49:9082; Ghantani, V. C. et al, Green Chem. (2013) 15:1211; Hong, J.-H. et al, Appl. Catal., A (2011) 396:194). Alternatively, pyrolysis of alkyl 2-acetoxy propanoate derivatives, which can be obtained from alkyl lactates directly by acetylation, also has been demonstrated to give the corresponding alkyl acrylates in varying yields with acetic acid as a coproduct (U.S. Pat. No. 2,477,293; Smith, L. T. et al, Ind. Eng. Chem. (1942) 34:473-479; Fisher, C. H. et al, J. Am. Chem. Soc. (1943) 65:763-767; Fein, M. L. et al, J. Am. Chem. Soc. (1944) 66:1201-1203; Filachione, E. M. et al, J. Am. Chem. Soc. (1944) 66:494-496; Fisher, C. H. et al, Ind. Eng. Chem. (1944) 36:229-234; Ratchford, W. P. et al, Ind. Eng. Chem. (1945) 37:382-387; Nezam, I. et al, Org. Process Res. Dev. (2017) 21:715-719). The nature of the alkyl (R) group of the starting lactate was shown to significantly affect the yield of the acrylate ester obtained (Burns, R. et al, J. Chem. Soc. (1935) 400-406; Rehberg, C. E. et al, J. Am. Chem. Soc. (1945) 67:56-57). Nickel catalyzed acetylation of lactide (the cyclic dimer of lactic acid) with acetic acid has been shown to give 2-acetoxypropionic acid, which can be subsequently pyrolyzed to give acrylic acid or converted to the methyl ester for production of methyl acrylate (U.S. Pat. No. 9,290,430). This route is attractive in that it gives high yields of acrylic acid or methyl acrylate from lactide, and utilizes readily available nickel(II) nitrate and nickel(II) acetate as the acetylation catalysts, but requires somewhat harsh conditions.
Currently, acrylic esters are derived from acrylic acid directly, which itself is produced from the oxidation of propene, a byproduct of ethylene and gasoline production, and requires expensive transition metal catalysts and high temperatures. Moving away from petroleum based feedstocks towards a biorenewable starting material is of key interest. The catalytic conversion of alkyl lactates into acrylate esters may have good potential for entry into the bio-renewable chemical commodity market. The shift away from petroleum chemical feedstock is an increasing driving force in the global market. Existing technologies can be complemented by the methods described herein.